Fan Blade Pass Frequency

Overview

Engineering reference data for Fan Blade Pass Frequency in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Example: Blade Pass Frequency Calculation

A fan with 10 blades rotating at 2400 rpm has a Blade Pass Frequency calculated as:

$BPF = \frac{n \cdot t}{60} = \frac{2400 \times 10}{60} = 400 \text{ Hz}$

Important Considerations

Sound Energy Characteristics

The energy concentrated at the Blade Pass Frequency can be very high and potentially annoying for surrounding areas, especially in fans with fewer blades. This tonal noise often stands out from the broadband fan noise spectrum.

Measurement Notes

• The Blade Pass Frequency may not be visible in standard fan noise charts
• Fan noise is typically documented in octave bands, which can mask discrete tonal components like BPF
• When analyzing fan noise, consider both the broadband spectrum and discrete tones separately

Design Implications

To reduce BPF-related noise issues:

• Increase the number of blades (raises frequency above audible annoyance range)
• Ensure adequate clearance between blade tips and housing
• Consider blade spacing variations to spread tonal energy

References

• Original Source